Catalytic production of polyamides from aromatic diamines

ABSTRACT

A method of producing a polyamide which is of sufficiently high molecular weight to be used in moulding applications or for film or fiber formation from an aromatic diamine, by a high temperature melt procedure comprises heating a diamine component comprising at least one bis(aminophenyl)sulphone with a diacid component comprising at least one dicarboxylic acid at a temperature of from 160* to 300*C under an inert atmosphere and in the presence of a catalytic amount of a salt of hypophosphorous acid and an organic base having a pKa of less than 3, the salt being put in the reaction mixture before the latter reaches 150*C. Preferably the organic base is the bis(aminophenyl)sulphone used as the diamine component and the salt is formed in situ by addition of the hypophosphorous acid or a compound or compounds which will produce this acid in the reaction mixture.

ited States Patent 1 Jones et'al.

[ 51 Mar. 27, 1973 [54] CATALYTIC PRODUCTION ,OF

POLYAMIDES FROM AROMATIC DIAMINES [73] Assignee: Imperial ChemicalIndustries Limited, London, England [22] Filed: Apr. 19, 1971 [21] Appl.No.: 135,500

Related U.S. Application Data [63] Continuation of Ser. No. 839,075,July 3, 1969,

3,206,438 9/1965 Jamison ..260/78 R 3,322,728 5/1967 Hill et al.3,505,296 4/1970 Burrows et al ..260/78 R Primary Examiner-Harold D.Anderson Att0rney-Cushman, Darby & Cushman [57] ABSTRACT A method ofproducing a polyamide which is of sufficiently high molecular weight tobe used in moulding applications or for film or fiber formation from anaromatic diamine, by a high temperature melt procedure comprises heatinga diamine component comprising at least one bis(aminophenyl)sulphonewith a diacid component comprising at least one dicarboxylic acid at atemperature of from 160 to 300C under an inert atmosphere and in thepresence of a catalytic amount of a salt of hypophosphorous acid and anorganic base having a pK of less than 3, the salt being put in thereaction mixture before the latter reaches l50C. Preferably the organicbase is the bis(aminophenyl)sulphone used as the diamine component andthe salt is formed in situ by addition of the hypophosphorous acid or acompound or compounds which will produce this acid in the reactionmixture.

7 Claims, No Drawings CATALYTIC PRODUCTION OF POLYAMIDES FROM AROMATICDIAMINES polyamides from aromatic diamines by high temperature meltprocedure has presented special problems because of their much slowerreaction with dicarboxylic'acids compared with aliphatic diamines andbecause their polyamides with dicarboxylic acids tend to undergo thermaldegradation at the temperatures required for a high temperature meltprocess. Thus, the rate of decomposition tends to offset the rate ofpolymerization before the required molecular weight for mouldingapplications or film or fiber formation has been attained.

Some proposals have been made for alleviating this problem but to ourknowledge no commercial process for the production of polyamides fromaromatic diamines by high temperature melt procedures has ever beendeveloped. One proposal, found in British Pat. specification 543843, hasbeen to add to the polycondensation mixture an acid catalyst having adissociation constant of more than 2 X for example phosphoric,sulphuric, hydrochloric or p-toluene sulphonic acid.

However, attempts to apply the use of any of these catalysts to theproduction of polyamides from bis(aminophenyl) sulphones have eitherfailed to provide products of adequate molecular weight because the rateof reaction has not been increased sufficiently to offset the competingdecomposition reaction, or else the required molecular weight has onlybeen achieved by use of uneconomically extended reaction times leadingto consequent loss of quality, e.g. discoloration, of the product.

More recently, manganous hypophosphite has been proposed for the samepurpose in the specificationof U.S. Pat. No. 3211705, but similarresults are obtained with this catalyst when applied to the productionof polyamides from bis(aminophenyl)sulphones. Moreover, the use of thiscatalyst tends to leave metallic residues in the polymeric product andthis can be undesirable for some applications.

We have now found that polyamides having the necessary molecular weightfor moulding applications and/or for film and/or fiber formation may beobtained from bis(aminophenyl) sulphonesby high temperature meltprocedures by use as catalyst of a salt of hypophosphorous acid (H,PO,)and an organic base having a pK, of less than 3.0 and preferably lessthan 2.5, where K, is the dissociation constant of a base, B, in termsof the equilibrium of the base and its conjugate acid, 811*, with asolvated proton:

According to the present invention, therefore, we provide a method ofproducing a polyamide suitable for use in moulding applications or forconversion to film or fiber which comprises heating a reaction mixturecomprising a diamine component comprising at least one bis(aminophenyl)sulphone or amide forming derivative thereof and a substantiallyequimolar amount of a diacid component comprising at least onedicarboxylic acid or amide forming derivative thereof at a temperatureof from 160 to 300C under an inert atmosphere andin the presence of acatalytic amount of a salt of hypophosphorous acid and an organic basehaving a pl(, of less than 3.0, and preferably less than 2.5, which saltis present in the reaction mixture before the latter reaches 150C.

Most preferably, the organic base is a compound having the formula asoamu where R is a monovalent hydrocarbon group or an amino-substitutedderivative thereof, and Ar is a divalent aromatic group, preferablyphenylene. Very suitably, the base is the same bis(aminophenyl)sulphonewhich is to be used in the polycondensation to form the polyamide. lnthis case, the salt need not be preformed before addition to thereaction mixture but may be formed in situ, e.g. by including in thereaction mixture hypophosphorous acid or a compound or mixture ofcompounds which will produce hypophosphorous acid in the polymerizationmixture before same reaches 150C.

Examples of other bases whose salts with hypophosphorous acid may beused in the polymerization according to our invention include, forexample, 2- and 4-acetylanilines, 4(p-aminobenzoyl)aniline, 4-benzoylaniline, 3- and 4-methylsulphonylanilines, haloanilines,cyanoanilines and nitroanilines.

The dicarboxylic acid used in the polycondensation is preferablyaliphatic, and especially adipic acid, sebacic acid, azelaic acid,pimelic acid, suberic acid or other a,wpolymethylene dicarboxylic acid,preferably having from six to 16 carbonatoms in all. A mixture of two ormore acids may be used if desired and the acid or acids may be replacedby their diphenyl esters, if desired.

The bis(aminophenyl)sulphone to be polycondensed may be,for example,4,4', 3,3'-, or 3,4- diaminodiphenyl sulphone. Mixtures of two or morebis(aminophenyl)sulphones may be used, if desired, and it is preferredthat the bis(aminophenyl)sulphone form substantially all of the diaminecomponent.

The diamine and dicarboxylic acid components of the mixture should bepresent in equimolar or substantially equimolar proportions where veryhigh molecular weight products are desired. However, a small excess ofeither, e.g. up to 5 mole percent, may be used without the molecularweight falling below the desired level; usually equivalent to a reducedviscosity (measured on a solution of l g of polymer in ml. of a 5 weightpercent solution of lithium chloride in dimethylformamide) of at least0.8.

The catalyst or precursor therefor, may be mixed with either of thepolyamide forming components of the polymerization mixture before thetwo components are mixed together or it may be added to the mixture. Itmay be added before or after heating has commenced but it must be addedbefore the mixture attains C. If the catalyst or precursor is added tothe mixture with the latter above this temperature, little or no benefitwill be obtained.

Only very small quantities of catalyst are required to gain benefittherefrom, for example equivalent to from 0.01 to 1 part ofhypophosphorous acid per 100 parts by weight of the mixture of diamineand diacid. Smaller or larger amounts may be used if desired but below0.005 part the effect may be small and above about 3 parts little or nofurther benefit is likely to be obtained.

A conventional melt polymerization procedure for polyamides may be used.Thus, for example, the diamine component, dicarboxylic acid componentand catalyst (or precursor therefor, e.g. hypophosphoric acid) may becharged simultaneously or in any order to a suitable reaction vesselfrom which the air has already been, or is thereafter, removed, and arethen heated at the appropriate reaction temperature, if necessary withthe application of vacuum, until the desired molecular weight has beenachieved. Suitably, the reaction is carried out under nitrogen or otherinert gas. Polymer formation will usually be accompanied by an increasein the viscosity of the melt and the degree of polymerization may bedetermined by measuring the melt viscosity. As the polymerizationproceeds, it may be found desirable or even necessary to raise thetemperature of the mixture in order to maintain it in molten form. Thepolymerization temperature required will depend to some extent on thenature of the dicarboxylic acid component of the polymerizable mixturebut in general temperatures within the range 160 to 300C will be foundsuitable. Preferred temperatures generally lie in the range 220 to 270C.

Preferably, at least the latter part of the reaction is effected undervacuum in order to aid the removal of the by-products of thepolycondensation. Preferably, also, the reaction is effected in twostages, the first of which is effected at a temperature of 160 to 240C,preferably under reflux so as to reduce any loss of acid bydistillation, and the second of which is effected at a temperature whichis higher than that of the first stage and is generally in the range 200to 270C. Preferably, the second stage is effected under a vacuumequivalent to an absolute pressure of 1.0 mm of mercury absolute orless.

Where a,w-polymethylene dicarboxylic acids having from six to 16 carbonatoms in all are polycondensed with the bis(aminophenyl) sulphones, thepolyamide products of the invention are generally mouldable amorphousmaterials which may be injection, compression, or transfer-moulded, orextruded into shaped articles, e.g. fibers, films and thick-walledarticles. The products from aromatic dicarboxylic acids are generallyconvertible to films, fibers and coatings from solution in suitablesolvents.

Before shaping, the polymers may be mixed if desired with any of theusual polymer additives, e.g. heat and light stabilizers, lubricants,fillers, mouldrelease agents and plasticizers, and may be blended withother polymeric materials, natural or synthetic.

The invention is illustrated by the following Examples. The4,4-diaminodiphenyl sulphone used in the Examples is available froml.C.l. Ltd. under the trade name of "Dapsone B.P.." The azelaic acidused was Emery Chemical Companys Emerox 1144."

EXAMPLE 1 The salt of hypophosphorous acid and bis(4-aminophenyl)sulphone was prepared by dissolving 5 parts of the diaminein a 50 percent aqueous solution of the acid; the amount of acid usedbeing chosen to be about two moles/mole of diamine. The reaction wasexothermic. The mixture was then cooled in ice whereupon the saltcrystallized. It was dried under high vacuum at room temperature andfound to have a melting point (with decomposition) of 104-107C.Elemental analysis showed a phosphorous content of 16.24 percent and anitrogen content of 7.45 percent by weight. Theory requires 16.3 percentand 7.4 percent respectively for C H O N P S.

24.83 Parts (100 molar parts) of dry bis(4- aminophenyl)sulphone and19.20 parts (102 molar parts) of azelaic acid were mixed together in apolymerization tube under an atmosphere of nitrogen. 0.1256 Part of thesalt was added and the mixture heated in a fluidized sand bath at 188C.After melting,

the reactants were agitated by passing a rapid current of nitrogenthrough the mixture.

Heating was continued at this temperature for 30 minutes during whichtime some water and a little azelaic acid distilled off and theviscosities of the mixture increased. The temperature was thenprogressively raised to 220C over 1% hours. Vacuum was then graduallyapplied as the temperature was raised to 260C at which point a finalvacuum of 0.3 mm of Hg absolute pressure was achieved. A slow passage ofnitrogen through the melt was continued for a further 2 hours with thetemperature maintained at 260C. After cooling, a rigid tough polymerfoam was recovered which had a reduced viscosity of 1.3 (measured on asolution of 1 g of polymer in 100 ml of 5 wt LiCl in dimethylformamideat 25C).

By way of comparison, the use of the corresponding saftfforii animating.4 4) yielded a polymer having a reduced viscosity of 0.39 and the use ofthe salt from 2,2-bis(4-aminophenyl) propane produced a similar result.

EXAMPLE 2 The polymerization process of Example 1 was re peated butusing 0.0514 part of a 50 weight percent aqueous solution ofhypophosphorous acid (H PO The time for heating to 220C was raised fromto minutes and the time at 260C was reduced to 1% hours.

The final product was a rigid, tough foam.

The reduced viscosity, measured as described in Example l, was 2.22 at25C.

Films obtained by compression moulding at 250C for 3 minutes weretransparent, strong and tough. No crystallinity was detected by X-rayexamination of the films.

By way of comparison, two further melt polymerizations were effected,one in the absence of any catalyst and the other using manganoushypophosphite as catalyst.

In each polymerization, 24.80 parts of bis(4- aminophenyl) sulphone and18.82 parts of azelaic acid were heated together in a polymerizationtube to C under an atmosphere of nitrogen and this temperature wasmaintained for 80 minutes during which time a little water and some aciddistilled off. The melt was agitated by passing a rapid current ofnitrogen through it. The temperature was then raised progressively to220C and held there for a further 70 minutes. The temperature was thenraised to 260C and the pressure reduced to 0.2 mm of Hg absolute, andpolymerization was continued under these conditions for 6 hours dur ingwhich time there was a slow increase in the viscosity of the melt. Atthe end of this period, the product was cooled and removed from thepolymerization tube.

The reduced viscosity of the polymer obtained from the uncatlyzed meltpolycondensation was 0.18 (measured as described above). In the secondcase, where 0.65 part of manganous hypophosphite was included in thepolymerizable mixture, the reduced viscosity of the product was 0.43.

In a series of further comparative experiments hypophosphorous acid wasreplaced by hydrochloric acid, sulphuric acid and p-toluene sulphonicacid respectively, the other conditions being unchanged. In-

all cases, the rates of polymerization were slower than in the case ofhypophosphorous acid and it was not possible to obtain products ofadequately high molecular weight.

EXAMPLE 3 49.66 Parts (100 molar parts) of bis(4-aminophenyl)sulphoneand 37.70 parts (100 molar parts) of azelaic acid were mixed with 0.103part of a 50 percent aqueous solution of hypophosphorous acid and heatedin a polymerization tube under reflux at 189C under a slow stream ofnitrogen for 1% hours. The water of reaction which was evolved wasreturned to the reaction zone, carrying with it any free azelaic acidwhich had been lost. The viscosity of the melt increased during thistime and evolution of azelaic acid ceased. The temperature was raised to240C and water gradually distilled off over a 60 minute period. Thetemperature was then raised further to 265C and a vacuum of 0.3 mm. ofHg absolute pressure applied, the reaction being continued under theseconditions for a further 2% hours. The viscosity increased rapidly onapplication of vacuum, finally becoming so viscous that nitrogen gascould not be drawn through the melt.

After cooling, the foamed reaction mass was removed from thepolymerization tube and powdered. The reduced viscosity, measured asdescribed in Example l, was 1.85. The melt viscosity of this polymer,measured on a Weissenburg Rheogoniometer at 270C and a shear rate of1.78 seewas 13 X poise and was unchanged after 15 minutes at thistemperature.

EXAMPLE 4 24.83 Parts of bis(4-aminophenyl)sulphone and 23.03 parts (anexactly equimolar amount) of decamethylene dicarboxylic acid were mixedwith 0.05 part of a 50 percent aqueous solution of hypophosphorous acidand reacted as in Example 3 to give a polymer having a reducedviscosity, as measured in Example 1, of 1.57.

EXAMPLE 5 24.8 Parts of bis(3-aminophenyl)sulphone (melting point174175C), 14.7 parts of polymer grade adipic acid and 0.033 part of a 50percent aqueous solution of hypophosphorous acid were mixed together atroom temperature under nitrogen and then subjected to the followingsequence, the mixture being maintained under nitrogen throughout:

i. heated to 185C and maintained there for 15 minutes,

ii. raised to 220C and maintained there for minutes,

iii. pressure reduced to 0.2 mm of Hg absolute and temperature raised to260C,

iv. 260C maintained for 75 minutes.

On cooling, a polyamide was recovered which was soluble in hot formicacid, cold dimethylformamide, cold dimethyl sulphoxide and coldconcentrated sulphuric acid. Its reduced viscosity (measured asdescribed in Example 1) was 1.05 and its second order glass/rubbertransition temperature (measured by differential thermal analysis) wasC.

X-ray examination showed the polymer to be amorphous.

Its melt viscosity at 270C and 10- seconds was 10 poises (measured on aWeissenburg Rheogoniometer).

EXAMPLE 6 The process of Example 5 was repeated using 4.75 parts of thediamine, 3.68 parts of azelaic acid and 0.009 part of the aqueoussolution of hypophosphorous acid. Stage (iv) of the treatment wasextended to 135 minutes.

The product had a melt viscosity of 6 X 10 poises at 270C and 10'(measured on a Weissenburg Rheogoniometer) indicating that it was ofvery high molecular weight. Differential thermal analysis showed asecond order glass/rubber transition temperature at 125C, and X-rayexamination showed the polymer to be amorphous. The second orderglass/rubber transition temperature at 125C was also observed usingdynamic mechanical techniques with a torsion pendulum.

0.005 inch thick films were prepared by compression moulding the driedpolymer at 250C. These films were strong and transparent and could becreased repeatedly without fracture, and X-ray examination showed thatno crystallization had occurred during compression moulding. Samples ofthe film that had been immersed in refluxing toluene for 4 hours,however, exhibited slight crystallinity on X-ray examination.

EXAMPLE 7 24.83 Parts of bis(4-aminophenyl)sulphone, 16.0 parts ofpimelic acid and 0.099 part of a 50 percent aqueous solution ofhypiphosphorous acid were mixed at room temperature under nitrogen andthe mixture was then subjected to the following series of treatments,all under nitrogen.

i. heated to 180C and maintained there for 30 minutes at atmosphericpressure,

ii. raised to 200C and maintained there for 45 minutes at atmosphericpressure,

iii. raised to 220C and maintained there for 25 minutes at atmospherepressure,

iv. pressure reduced to 0.1 mm of Hg absolute and temperature raised to260C, v. temperature maintained at 260C for 2 hours. After cooling, apolymer was recovered having a reduced viscosity (measured as describedin Example 1) of 1.06.

EXAMPLE 8 Two hundred and forty-eight Parts of bis(3-aminophe'nyl)sulphone, 23.2 parts of decamethylene dicarboxylic acid and0.04 part of a 50 percent aqueous solution of hypophosphorous acid werereacted as described in Example 5 to give a polymer having a reducedviscosity (measured as described in Example 1) of 0.87. X-rayexamination of the product showed it to be amorphous and differentialthermal analysis indicated a second order glass/rubber transitiontemperature at 107C.

EXAMPLE 9 24.8 Parts of bis(4-aminophenyl)sulphone, 15.2 parts ofazelaic acid and 3.3 parts of isophthalic acid were mixed bytumble-blending the dry powders. 0.125 part of a 50 weight percentaqueous solution of hypophosphorous acid was added and tumble blendedwith the mixture for 5 minutes. The mixture was then heated to 180Cunder a stream of dry nitrogen after minutes the temperature was raisedto 220C. Water distilled off over a period of 40 minutes at thistemperature and then the pressure was gradually reduced over a period of25 minutes to 0.2 mm of Hg absolute. The temperature was then raised to250C and maintained there for 2% hours. The mass was then cooled and thepolymer recovered as a tough pale yellow polymeric foam having a reducedviscosity, measured as in Example 1, of 2.13. X-ray examination showedthe polymer to be amorphous and its glass/rubber transition temperaturewas 193C.

EXAMPLE 10 A mixture of 24.8 parts of bis(4-aminophenyl)sulphone, 20.2parts of sebacic acid and 0.102 part of a 50 weight percent aqueoussolution of hypophosphorous acid was heated to 180C under a slow streamof nitrogen in a polymerization tube. After a few minutes, a homogeneouspale yellow melt had formed which was stirred by the passage ofnitrogen. The temperature was maintained at 180C for 30 minutes duringwhich time water steadily distilled over. The temperature was thenraised to 200C for 45 minutes and then to 220C for 25 minutes. At thistime vacuum was gradually applied as the temperature was raised to 260C.After 1 hour at 260C under a vacuum corresponding to an absolutepressure of 0.15 mm of Hg. the polymer had formed a highly viscous foam.The heat was removed and the product recovered. lts reduced viscosity,measured, as in Example 1, was 1.27.

We claim:

1. A method of producing a fiber or film-forming or mouldable polyamidewhich comprises heating a reaction mixture in which the principaldiamine component is at least one bis(aminophenyl) sulphone and asubstantially equimolar amount of at least one 01,0)-

pol meth lene dicarboxylic acid havingf six to sixteen car on a oms mall at a temperature 0 from 160 to 300C. under an inert atmosphere andin the presence of, as catalyst, a salt of hypophosphorous acid andbis(aminophenyl)sulphone having a pK of less than 3.0, said salt beingpresent in the reaction mixture before the latter reaches C.

2. A method as claimed in claim 1 in which the bis( aminophenyl)sulphoneportion of the catalyst has a pK, of less than 2.5.

3. A method as claimed in claim 1 in which the bis(aminophenyl)sulphoneportion of the catalyst is bis (4- or 3-aminophenyl)sulphone.

4. A method as claimed in claim 1 in which the salt is present in anamount equivalent to from 0.005 to 3 parts of hypophosphorous acid per100 parts of the mixture of diamine and diacid.

5. A method as claimed in claim 4 in which the salt is present in anamount equivalent to from 0.01 to 1 part of hypophosphorous acid per 100parts of the mixture of diamine and diacid.

6. A method as claimed in claim 1 in which the reaction mixture isheated at a temperature of from 220 to 270C.

7. A method as claimed in claim 6 in which the reaction mixture issubjected to a first stage at which it is heated to a temperature offrom to 240C.

I i IR

2. A method as claimed in claim 1 in which the bis(aminophenyl)sulphone portion of the catalyst has a pKa of less than 2.5.
 3. A method as claimed in claim 1 in which the bis(aminophenyl)sulphone portion of the catalyst is bis (4- or 3-aminophenyl)sulphone.
 4. A method as claimed in claim 1 in which the salt is present in an amount equivalent to from 0.005 to 3 parts of hypophosphorous acid per 100 parts of the mixture of diamine and diacid.
 5. A method as claimed in claim 4 in which the salt is present in an amount equivalent to from 0.01 to 1 part of hypophosphorous acid per 100 parts of the mixture of diamine and diacid.
 6. A method as claimed in claim 1 in which the reaction mixture is heated at a temperature of from 220* to 270*C.
 7. A method as claimed in claim 6 in which the reaction mixture is subjected to a first stage at which it is heated to a temperature of from 160* to 240*C. 